Providers of telephony services maintain a pool of phone numbers that are assigned to endpoints associated with their subscribers. These phone numbers may be reassigned when, for example, a subscriber's subscription is terminated or when an endpoint associated with a subscriber is repurposed, replaced, or eliminated. Before reassigning a phone number, most service providers quarantine the number for a period of time (e.g., six months) to allow for the number to become disassociated with the former endpoint or subscriber. During this quarantine period, calling parties are typically notified that the number is no longer in service. Once the quarantine period ends, the number is placed back in the pool of phone numbers and made available for reassignment. The basic premise of this approach is that passage of the quarantine period in combination with the notification of callers during the quarantine period makes it less likely that the new subscriber to which the number is reassigned will receive calls intended for the old subscriber.
While this approach may reduce the likelihood that calls intended for one party are received by another, it is often ineffective. That is, the quarantine period is typically not long enough to ensure that all parties who might call the previous subscriber become aware of the change. This results in connections being made that are frustrating and disruptive to both the calling party and the new subscriber. Telephony service providers can increase the quarantine period to further reduce the likelihood of such connections. However, there is an ongoing cost to the provider for maintaining control of each phone number that cannot be recouped during the period when the number is quarantined.